Tracking systems for optically measuring the location or position of an object within a field of view have been developed for numerous applications. These tracking systems typically require the measurement of very small changes in the angle of incidence of light from the object being tracked. Autocollimators for example, are optical instruments used for measuring the movement of a distant reflecting surface. The basic principle of the autocollimator is that of observing the coincidence of an illuminated reticle or slit with its own image reflected from the distant reflector back through the instrument. When coincidence is observed, the distant reflector is accurately positioned perpendicular to the optical axis of the instrument. If the distant reflector is not perpendicular to the optical axis of the instrument, the reflected light will be displaced from the slit. The displacement of the reflected light is a measure of the angular deviation of the returning light beam which can be correlated with the angular deviation of the distant reflector.
The use of available autocollimators to provide tracking of the movement of objects has many limitations. Autocollimators are generally relatively large and thus may be inappropriate for applications having size constraints. Additionally, with a 0.5 microradian resolution and a 2 microradian repeatability, the accuracy and repeatability of available autocollimators is not suitable for extremely high precision applications. Furthermore, autocollimators typically require several seconds for a single measurement. Also, the noise level of present autocollimators may be too high for certain applications.
Accordingly, there is a continuing need for an improved optical tracking system that is compact, provides enhanced accuracy, resolution and operational speed at low noise levels.